Method of separating carbazole from anthracene oil



United States Patent ()fi 3,070,517 Patented Dec. 25, 1962 ice 3,070,517 METHOD OF SEPARATING CARBAZOLE FROM ANTHRACENE OIL Gerald Gilbert, Pittsburgh, and Robert M. Stickel, Franklm Township, Westmorelaud County, Pa., assignors to lflmted States Steel Corporation, a corporation of New ersey Filed Oct. 9, 1959, Ser. No. 845,423 2 Claims. (Cl. 202-395) This invention relates to a method for recovering carbazole from coal-tar distillate and, in particular, to a simple process which gives a good yield of high-purity carbazole at low cost.

Carbazole is a small (5%) but valuable component of the anthracene-oil fraction of coal tar. It has numerous uses but its recovery in a reasonably high state of purity has presented much difliculty. All the known methods are complex and expensive or give low yields of a product not sufiiciently pure for commercial acceptance, for which 95% purity is the minimum.

We have invented a novel process for separating carbazole from the components of anthracene oil which is very simple and inexpensive yet gives good yield of product better than 95% pure. In general terms, according to our invention, a carbazole-containing coal-tar fraction, such as that boiling from 315 to 355 C., is mixed with triethanolamine and distilled. The triethanolamine causes a marked change in the distillation characteristics of the mixture, in that the phenanthrene and anthracene no longer distill with the carbazole. This distillation yields a carbazole fraction containing practically no anthracene and phenanthrene, but having a high concentration of triethanolamine and oils. The triethanolamine is soluble in water and can be readily separated by washing the distilled carbazole fractions. The carbazole is reremoved from the oil by crystallization from xylene or another suitable solvent. Thus, the entire process for producing commercial carbazole from a crude material containing only about 5% carbazole involves only mixing the coal-tar fraction with triethanolamine, distilling to obtain the carbazole fraction, washing the carbazole fraction with water to remove triethanolamine, and crystallizing the washed carbazole fraction from xylene giving a product carbazole of about 98% purity.

A complete understanding of the invention may be obtained from the following detailed explanation of a practice typical thereof, which refers to the accompanying drawings in which:

FIGURE 1 is a graph showing the separation effected by our method; and

FIGURE 2 is a diagram showing apparatus for carry ing out the method on a commercial scale.

In a preferred practice of the invention, 225 grams of a coal-tar fraction boiling in the range 315 to 355 C. was mixed with 170 grams of triethanolamine. The resultant mixture was vacuum-distilled at 50 mm. Hg absolute pressure through a fractionating column (40 theoretical plates) at a reflux ratio of 9 to 1. Fourteen fractions were separately collected and water-washed to remove the triethanolamine. Analysis of the washed fractions indicated an almost complete separating of anthracene from carbazole. These data are shown in FIGURE 1. Combining fractions 2 through 10 to 60 weight percent distilled) gave a mixture predominantly anthracene (13.8 weight percent) and phenanthrene (48.4 weight percent) with very little carbazole (1.9 Weight percent). Fractions 11 and 12 combined gave a product predominantly carbazole (19.2 weight percent) and contained essentially no anthracene or phenanthrene. After removal of anthracene and phenanthrene, the remaining carbazole fraction can be easily upgraded to 98% purity (commercial grade) by crystallization from the usual solvents (xylene, dioxane, ethanol).

A more complete understanding of our invention and the procedures involved may be had by reference to FIG- URE 2. As shown therein, pipe 1 delivers a coal-tar creosote boiling from about 200 C. to about 360 C. at atmospheric pressure, continuously to a still A where it is distilled at 50 mm. Hg absolute pressure to obtain the fraction boiling over 210 C. (315 C. at atmospheric pressure). A lower-boiling fraction (light ends) is removed through line 2. The fraction boiling above 210 C. is taken as bottoms from still A through line 3 to a still B. In the latter, again at 50 mm. absolute pressure, the 210-245" C. fraction is taken overhead. A higher-boiling fraction (bottoms) is removed from still B through line 5. The fraction boiling between 210 and 245 C. is fed through line 4 to a still C. At the same time, triethanolamine is fed thereto through line 7. The resulting mixture is distilled continuously at 50 mm. Hg absolute pressure.

The heads fraction containing anthracene, phenanthrene and triethanolamine, is taken through line 6 to an extractor E, to which water is added through line 9. The water extracts the triethanolamine from the anthracenephenanthrene cake and carries the solvent to a still D through linell. The anthracene-phenanthrene cake is removed through line 10 to crystallizer F. Xylene, or another suitable solvent, is added to crystallizer F through pipe 12. Anthracene is recovered by crystallization and is removed from the crystallizer through pipe 13. In still D, the water is removed from the triethanolamine and piped to disposal through line 14. The triethanolamine is returned to feed line 7 through line 16.

The tail fraction from still C contains carbazole and triethanolamine and is carried from the still to an extractor E through line 8. The triethanolamine is extracted from the carbazole with water added through line 17. The water-triethanolamine solution is carried through line 15 to still D for recovery of the triethanolamine. The carbazole in extractor E is transferred through line 18 to a crystallizer P where it is upgraded to high purity by crystallization from xylene (or other suitable solvent) added through line 19. The carbazole is then discharged through line 20.

The conditions described represent those preferred for commercial use. Many of the conditions, however, may be varied without affecting the separation markedly. For example, the pressure of distillation may be as low as 10 mm. or as high as atmospheric pressure and still give an excellent separation of the anthracene and phenanthrene from the carbazole. At higher distillation pressures, some decomposition of the triethanolamine occurs. Therefore, the range 25 to mm. Hg, preferably 50 mm., where triethanolamine decomposition is negligible, is most desirable for operation of the process. The use of lower pressure does not markedly improve the efficiency of the process. In the most favorable mode of operation of our invention, the amount of triethanolamine in still C is maintained at between 15 and 60%, preferably about 40% by volume of the total material in this still. Concentrations of the amine below 40% may be used without affecting the degree of separation until concentrations as low as 15% of the charge are reached. Below that value, large amounts of anthracene and phenanthrene are found in the carbazole fraction.

It will be apparent that our invention provides a highly desirable method for carbazole recovery. The method is simple yet highly effective, giving good yields of highquality product carbazole. The anthracene fraction separated may also be purified to make it commercially saleable.

Although we have disclosed herein the preferred prac- 3 tice of our invention, we intend to cover as well any change or modification therein which may be made withoutd eparting from the spirit and scope of the invention.

We claim:

1. A method for separating carbazole from a coal-tar fraction boiling between 315 and 355 C. which comprises adding triethanolamine to said fraction until the amine constitutes from 15 to 60% by volume of the mixture, subjecting the resulting mixture to fractional distillation, collecting the carbazole-containing fraction remaining and extracting said amine therefrom with water.

2. A method of separating carbazole from anthracene 4 oil which comprises mixing triethanolamine with the oil to the extent of 15 to 60% by volume of the mixture, subjecting the mixture to fractional distillation, collecting the carbazole-containing fraction remaining and extracting the triethanolamine therefrom with water.

References Cited in the file of this patent UNITED STATES PATENTS 1,662,061 Hess et a1. Mar. 13, 1928 1,879,686 Jaeger et al. Sept. 27, 1932 1,892,772 Jaeger et al. Jan. 3, 1933 2,590,096 Feldman et al Mar. 25, 1952 2,675,345 Andrews Apr. 13, 1954 

1. A METHOD FOR SEPARATING CARBAZOLE FROM A COAL-TAR FRACTION BOILING BETWEEN 315 AND 355*C. WHICH COMPRISES ADDING TRIETHANOLAMINE TO SAID FRACTION UNTIL THE AMINE CONSTITUTES FROM 15 TO 60% BY VOLUME OF THE MIXTURE, SUBJECTING THE RESULTING MIXTURE TO FRACTIONAL DISTILLATION, COLLECTING THE CARBAZOLE-CONTAINING FRACTION 